ICMCTF2007 Session E2-2: Mechanical Properties and Adhesion

Wednesday, April 25, 2007 1:30 PM in Room California

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	E2-2-1 Diffusion-Multiple Approach to Alloy and Coating Development J.-C. Zhao (GE Global Research) The diffusion-multiple approach consists of creation of composition gradients and intermetallic phases by long-term annealing of junctions of three or more phases/alloys and mapping various properties to establish phase diagrams and composition-structure-property relationships. It can be used to effectively collect data for alloy and coating development. Some of the valuable data/information that can be obtained from diffusion multiples include phase diagrams, diffusion coefficients, precipitation kinetics, solution-strengthening effects, precipitation-strengthening effects, point defect propensity, and others. The coupling of the diffusion-multiple approach with the CALPHAD approach can have a big impact on computational design of alloys and coatings. Examples will be shown to illustrate the progress made to date on applying the diffusion-multiple approach to accelerated design of alloys and coatings.
2:10 PM		E2-2-3 Microstructure and Mechanical Properties of Zr-Cu Based Thin Films Deposited by Pulsed Magnetron Sputtering O. Jimenez, A. Leyland, M. Audronis, A. Matthews (University of Sheffield, United Kingdom); M.A. Baker (University of Surrey, United Kingdom) This paper presents results on zirconium-copper based thin films deposited by pulse dc unbalanced magnetron sputtering from two planar targets in an atmosphere of Ar and Ar+N₂ at a total pressure of 0.8 Pa. The low-miscibility binary Zr-Cu system permits the deposition of nanocomposite coatings with the addition of nitrogen as solution hardening (and/or nitride-forming) element, consisting of Zr(N) transition metal grains (or a ZrN transition metal nitride), surrounded by a minority low modulus, immiscible, amorphous intergranular metallic phase (Cu). The samples were placed inside the deposition chamber at different target-to-substrate distances using a range of nitrogen flow rates, which resulted in coatings with different chemical composition. The microstructure of these coatings has been studied by means of x-ray diffraction, scanning electron microscopy and transmission electron microscopy. Nanoindentation measurements were taken to observe on the mechanical properties such as hardness and elastic modulus. Changes in the microstructure and correlations between this and mechanical properties are presented.
2:30 PM		E2-2-5 Study of the Evolution of the Mechanical Properties of a Silicon Single Crystal after Femtosecond Laser Irradiation S. Valette (Ecole Centrale de Lyon, France); S. Benayoun, P. Kapsa (Laboratoire de Tribologie et Dynamique des Systemes, France); R. Fillit (Ecole des Mines de Saint-Etienne, France); E. Audouard (Laboratoire de Traitement du Signal et Instrumentation, France) The aim of this work is to study the modifications of the mechanical and structural properties of a single crystal silicon wafer, induced by a femtosecond laser surface treatment. Two regimes of illumination are compared in order to link the effects of the modifications on the surface of the material with the deposited energy. Nanoindentation experiments indicate a drastic decrease of the Young's modulus and of the hardness of this surface. The modification occurs on the range of the micrometer in depth. The roughness of the irradiated zones and the indent geometry are analysed with an AFM. AFM also provides studding of the microcracks generated by the Berkovich's tip on the brittle silicon single crystal. Femtosecond irradiation induces mechanical property modifications of the silicon. The more the deposited energy, the softer and less brittle the material is. Such a behavior may be associated with a nanocrystallization and/or an amorphisation of the silicon. Fore another, a high resolution X-ray diffraction study of the diffraction peak profile is proposed. A broadening of the (620) diffraction peak is obtained, this will be discussed.
2:50 PM		E2-2-6 Evaluation of PVD Coatings used in Aluminum Die Casting S. Myers, J. Lin (Colorado School of Mines); P. Reid (Ried and Associates, LLC); B. Mishra, J.J. Moore (Colorado School of Mines) The large thermal fatigue and corrosive environment encountered in aluminum pressure die casting often results in premature failure of dies, thus creating a cost factor that includes large quantities of scrap and productivity loss. Aluminum pressure die casters are currently using a wide variety of PVD die coatings in conjunction with surface treatments in an effort to prolong die life and die casting campaigns. This paper examines the degradation mechanisms, such as washout/erosion, soldering, and thermal fatigue cracking of several commercial and experimental coatings in addition to surface modification techniques, such as ferritic nitrocarburizing and ion nitriding that have been used on core pins and inserts in both die casting in-plant trials and several laboratory tests. The controlling degradation mechanisms will be discussed and promising potential die coating systems and duplex systems will be proposed.
3:10 PM	Invited	E2-2-7 Structural and Mechanical Characterization of Biomaterials - Lessons from Nature X. Li (University of South Carolina) Nature has long been using bottom-up nanofabrication methods to form self-assembled nanomaterials that are much stronger and tougher than many man-made materials formed top-down. One of the best examples is nacre. It has evolved through millions of years to a level of optimization not currently achieved in engineered composites. Nacre has a brick-and-mortar-like structure with highly organized polygonal aragonite platelets of a thickness ranging from 200 to 500 nm and an edge length about 5 micrometers sandwiched with a 5-20 nm thick organic biopolymer interlayer, which assembles the aragonite platelets together. The combination of the soft organic biopolymer and the hard inorganic calcium carbonate produces a lamellar composite with a 2-fold increase in strength and a 1000-fold increase in toughness over its constituent materials. Such remarkable properties have motivated many researchers to synthesize biomimetic nanocomposites that attempt to reproduce the achievements of nature and to understand the toughening and deformation mechanisms of natural nanocomposite materials. We developed a micro-mechanical tester that can be used inside an atomic force microscope. We performed tensile and bending tests on nacre in situ where the nacre surface was imaged simultaneously by the atomic force microscope. Here we report the discovery of nanosized grains (particles) in nacre. We reveal the toughening secrets in nacre - rotation and deformation of aragonite nanograins, absorbing energy in the deformation of nacre. This opens up opportunities to develop nacre-like ultra-tough materials. There is still a lot we need to learn from Nature.
3:50 PM		E2-2-10 Tribological Properties of Nanoscale Multilayer TiAlN/SiN Coating Deposited by Reactive Direct Current Magnetron Sputtering M. Sakurai, T. Toihara, M. Wang (Osg Corporation, Japan); W. Kurosaka, S. Miyake (Nippon Institute of Technology, Japan) The nanomultilayer TiAlN/SiN coatings were prepared on tool carbide substrates using a reactive direct current (DC) magnetron sputtering technique. A coating with a thickness of approximately 4 ïm was deposited by reactive DC magnetic sputtering while rotating the substrate in front of TiAl and Si targets. The investigation of hardness and scratch reveals that the mechanical properties of a multilayer coating with the basic nano-lamellae obtained as a result of substrate rotation in front of TiAl and Si targets were improved. Tribological studies of the TiAlN/SiN coatings were conducted using friction tester. Results indicated the mechanical and tribological properties of the nanomultilayer TiAlN/SiN coating were influenced by the period of a nanomultilayer coating.
4:10 PM		E2-2-9 Thermal Stabilities and Fracture Characteristics of Aged ZrAlN/TiN Heterostructure Film and ZrTiAlN Nano-Composite Film by Using Indentation Methods S. Baek (Sungkyunkwan University, Korea) ZrAlN/TiN heterostructure films(bilayer repeat period: 1.6nm(sample-1), 2.7nm(sample-2), 5.4nm(sample-3)) and ZrTiAlN nanocomposite films(N₂ pressure / grain size:1.0mTorr/ 3.75nm(sample-4), 1.5mTorr/3.55nm(sample-5), 3.5mTorr/2.85nm(sample-6)) were synthesized on Si(100) substrate by closed field unbalanced magnetron sputtering process, respectively. All the film thickness is fixed at a 1µm. To investigate the thermal stabilities and fracture characteristics of the films below 250°C with various thermal aging conditions, we thermally aged the films for different aging temperature (150, 200, 250°C) and time (0: virgin, 120, 240, 360 hours). The material properties and structures of the aged samples were investigated by using nano-indentation, micro-indentation, XRD and AFM. The maximum nanohardness value (28GPa) of virgin ZrAlN/TiN films can be obtained as the bilayer repeat period is 2.7nm, Sample-2. After aging, the material properties of the Sample-3 at 250°C(time:360hours) such as elastic modulus, nanohardness, H³ / E² and indentation fracture toughness are retained within the 85% of virgin material properties. But, these properties of the others ZrAlN/TiN films(Sample-1 and Sample-2) at 250°C(time: 360hours) extremely decreased. The calculated indentation fracture toughness of the aged ZrAlN/TiN films excluding the influence of the substrate was 3.3, 5.4, 8.3MPam^0.5, respectively. The nanohardness of virgin ZrTiAlN nanocomposite samples was measured to be in the range of 19 - 43GPa. But these films aged at 250°C (after 120hours) were extremely damaged by spalling, delamination and cracking. The results revealed that ZrAlN/TiN heterostructure films had better fracture characteristics and thermal stabilities than ZrTiAlN nano-composite films.
4:30 PM		E2-2-11 Nanoindentation Study of Nanocrystalline TiN Thin Films V. Chawla (Indian Institute of Technology Roorkee); R. Jayaganthan, R. Chandra (Indian Institute of Technology Roorkee, India) Nanocrystalline thin films possess enhanced mechanical and physical properties compared to that of its bulk counterpart. Particularly, Nanocrystalline TiN thin film has been identified as a potential material for tribological and diffusion barrier applications due its very high hardness, wear resistance, and metallurgical stability, and adhesion properties. It is very essential to investigate the mechanical properties of the nanocrystalline TiN thin films to ensure its compatibility and reliability for fabricating diffusion barriers in semiconductor devices and for its better tribological performance in cutting tools. Although numerous published works on TiN thin film is available in the literature, the deformation mechanisms operating in nanoscrystalline regime are poorly understood. Therefore, the present work is focussed to investigate the mechanical behaviour of DC sputtered nanocrystalline TiN thin films by Nanoindentation technique and render an insight into the deformation mechanisms through microstructural characterisations using AFM and TEM. The TiN thin films with thickness ranging from 0.1 to 1µm were deposited by DC magnetron sputtering on Si (100) wafer. XRD is used to identify the phases in TiN thin film deposited by using different process conditions in sputtering. Nanoindentation technique is used to evaluate the young's modulus and hardness of TiN thin films. The effect of substrate temperature (RT to 400°C) and biasing on the structure and mechanical properties of nanocrystalline TiN thin film is investigated. TiN thin film samples are tested with different load rates to evaluate the flow behaviour. The influence of pile-up and sink-in, during indentation, were considered in determining the real contact between the indenter and the specimens. The effect of thickness and microstructural morphology on the elastic and plastic behaviour of TiN thin film is discussed.